As previously mentioned, I’m translating excerpts from some letters from the 1830s which are written in a somewhat nonstandard orthography, very idiosyncratic punctuation, and sometimes with rather peculiar expressions.
I’m currently at a bit which describes a woman with the phrase (if a phrase it is) témoin agente, and I’m having a bit of trouble figuring what exactly that is. The context would seem to imply that it’s simply a witness, but since I can find exactly one instance of the word being used on the Internet, I don’t have any way of verifying that this is in fact so.
The phrase occurs at the beginning of a letter:
Constance, ma chère Natalie, me prie de vous dire que ses esprits ne sont pas assez concentrés pour pouvoir se mettre auteur, en rapportant les scènes, auquelles elle a été témoin agente depuis ses derniers ouvrages en forme de lettres; toutes plaintes ont cessés, car elle a reçu 4 lettres de la part de sa chère Maman…
The ‘scenes’ referred to here are mainly the fact that Constance’s infant child had just gone through a terrible ordeal, nearly dying from some unknown illness. Saying that she doesn’t feel up to writing letters just yet describing the scenes she’s witnessed sounds quite reasonable and logical.
According to TLFi,
L’emploi au fém. est exceptionnel. Ac. 1878 signale que „lorsque le mot est pris en mauvaise part, on lui donne quelquefois un féminin“ avec les ex. suiv. : „Elle est leur principale agente. Je découvris que dans cette intrigue, elle était la principale agente.“
Going by that, the usage in the letter is additionally odd in that it uses the decidedly nonstandard feminine form of the word. Looking for témoin agent in the masculine doesn’t reveal anything more useful, though—everything I can find is examples like “le témoin, agent de police, était…”, where the two words just happen to be right next to each other, but have nothing really to do with each other.
Agent itself comes from the Latin āgēns, which is the present participle of āgō ‘act, do’. If we take that straight down to Modern French, one might assume that it means an ‘acting/active witness’ (someone who is an active part in the goings-on described, I suppose)—but the Modern French outcome of āgō is agir, whose present participle is agissant, not agent, so that doesn’t seem a likely explanation either.